/** public domain  */
package org.xhtmlrenderer.simple.extend;



/**
 * Provides a method to encode any string into a URL-safe form. Non-ASCII
 * characters are first encoded as sequences of two or three bytes, using the
 * UTF-8 algorithm, before being encoded as %HH escapes.
 *
 * @author   Torbjoern Gannholm
 */
public class URLUTF8Encoder {

    /** Description of the Field */
    final static String[] hex = {
            "%00", "%01", "%02", "%03", "%04", "%05", "%06", "%07",
            "%08", "%09", "%0a", "%0b", "%0c", "%0d", "%0e", "%0f",
            "%10", "%11", "%12", "%13", "%14", "%15", "%16", "%17",
            "%18", "%19", "%1a", "%1b", "%1c", "%1d", "%1e", "%1f",
            "%20", "%21", "%22", "%23", "%24", "%25", "%26", "%27",
            "%28", "%29", "%2a", "%2b", "%2c", "%2d", "%2e", "%2f",
            "%30", "%31", "%32", "%33", "%34", "%35", "%36", "%37",
            "%38", "%39", "%3a", "%3b", "%3c", "%3d", "%3e", "%3f",
            "%40", "%41", "%42", "%43", "%44", "%45", "%46", "%47",
            "%48", "%49", "%4a", "%4b", "%4c", "%4d", "%4e", "%4f",
            "%50", "%51", "%52", "%53", "%54", "%55", "%56", "%57",
            "%58", "%59", "%5a", "%5b", "%5c", "%5d", "%5e", "%5f",
            "%60", "%61", "%62", "%63", "%64", "%65", "%66", "%67",
            "%68", "%69", "%6a", "%6b", "%6c", "%6d", "%6e", "%6f",
            "%70", "%71", "%72", "%73", "%74", "%75", "%76", "%77",
            "%78", "%79", "%7a", "%7b", "%7c", "%7d", "%7e", "%7f",
            "%80", "%81", "%82", "%83", "%84", "%85", "%86", "%87",
            "%88", "%89", "%8a", "%8b", "%8c", "%8d", "%8e", "%8f",
            "%90", "%91", "%92", "%93", "%94", "%95", "%96", "%97",
            "%98", "%99", "%9a", "%9b", "%9c", "%9d", "%9e", "%9f",
            "%a0", "%a1", "%a2", "%a3", "%a4", "%a5", "%a6", "%a7",
            "%a8", "%a9", "%aa", "%ab", "%ac", "%ad", "%ae", "%af",
            "%b0", "%b1", "%b2", "%b3", "%b4", "%b5", "%b6", "%b7",
            "%b8", "%b9", "%ba", "%bb", "%bc", "%bd", "%be", "%bf",
            "%c0", "%c1", "%c2", "%c3", "%c4", "%c5", "%c6", "%c7",
            "%c8", "%c9", "%ca", "%cb", "%cc", "%cd", "%ce", "%cf",
            "%d0", "%d1", "%d2", "%d3", "%d4", "%d5", "%d6", "%d7",
            "%d8", "%d9", "%da", "%db", "%dc", "%dd", "%de", "%df",
            "%e0", "%e1", "%e2", "%e3", "%e4", "%e5", "%e6", "%e7",
            "%e8", "%e9", "%ea", "%eb", "%ec", "%ed", "%ee", "%ef",
            "%f0", "%f1", "%f2", "%f3", "%f4", "%f5", "%f6", "%f7",
            "%f8", "%f9", "%fa", "%fb", "%fc", "%fd", "%fe", "%ff"
            };

    /**
     * Encode a string to the "x-www-form-urlencoded" form, enhanced with the
     * UTF-8-in-URL proposal. This is what happens: <p/>
     *
     *
     * <ul>
     *   <li> <p>
     *
     *   The ASCII characters 'a' through 'z', 'A' through 'Z', and '0' through
     *   '9' remain the same. <p/>
     *
     *
     *   <li> <p>
     *
     *   The unreserved characters - _ . ! ~ * ' ( ) remain the same. <p/>
     *
     *
     *   <li> <p>
     *
     *   The space character ' ' is converted into a plus sign '+'. <p/>
     *
     *
     *   <li> <p>
     *
     *   All other ASCII characters are converted into the 3-character string
     *   "%xy", where xy is the two-digit hexadecimal representation of the
     *   character code <p/>
     *
     *
     *   <li> <p>
     *
     *   All non-ASCII characters are encoded in two steps: first to a sequence
     *   of 2 or 3 bytes, using the UTF-8 algorithm; secondly each of these
     *   bytes is encoded as "%xx".
     * </ul>
     *
     *
     * @param s  The string to be encoded
     * @return   The encoded string
     */
    public static String encode( String s ) {
        StringBuffer sbuf = new StringBuffer();
        int len = s.length();
        for ( int i = 0; i < len; i++ ) {
            int ch = s.charAt( i );
            append( sbuf, ch );
        }
        return sbuf.toString();
    }

    /**
     * Description of the Method
     *
     * @param chars  PARAM
     * @return       Returns
     */
    public static String encode( char[] chars ) {
        StringBuffer sbuf = new StringBuffer();
        int len = chars.length;
        for ( int i = 0; i < len; i++ ) {
            int ch = chars[i];
            append( sbuf, ch );
        }
        return sbuf.toString();
    }

    /**
     * Description of the Method
     *
     * @param sbuf  PARAM
     * @param ch    PARAM
     */
    private static void append( StringBuffer sbuf, int ch ) {
        if ( 'A' <= ch && ch <= 'Z' ) {// 'A'..'Z'
            sbuf.append( (char)ch );
        } else if ( 'a' <= ch && ch <= 'z' ) {// 'a'..'z'
            sbuf.append( (char)ch );
        } else if ( '0' <= ch && ch <= '9' ) {// '0'..'9'
            sbuf.append( (char)ch );
        } else if ( ch == ' ' ) {// space
            sbuf.append( '+' );
        } else if ( ch == '-' || ch == '_' // unreserved
                || ch == '.' || ch == '!'
                || ch == '~' || ch == '*'
                || ch == '\'' || ch == '('
                || ch == ')' ) {
            sbuf.append( (char)ch );
        } else if ( ch <= 0x007f ) {// other ASCII
            sbuf.append( hex[ch] );
        } else if ( ch <= 0x07FF ) {// non-ASCII <= 0x7FF
            sbuf.append( hex[0xc0 | ( ch >> 6 )] );
            sbuf.append( hex[0x80 | ( ch & 0x3F )] );
        } else {// 0x7FF < ch <= 0xFFFF
            sbuf.append( hex[0xe0 | ( ch >> 12 )] );
            sbuf.append( hex[0x80 | ( ( ch >> 6 ) & 0x3F )] );
            sbuf.append( hex[0x80 | ( ch & 0x3F )] );
        }
    }

}

